Metal casting apparatus

ABSTRACT

A crucible having a bottom outlet opening with heating means disposed about the sidewall and downwardly as far as the outlet, mold supporting means beneath the crucible outlet, a gate for closing and opening the outlet, the underside of the bottom of the crucible being concave and the gate comprising a pair of upwardly convex members in movable sealing engagement with the underside of the crucible bottom and having the same curvature as the concave underside, whereby the outlet and gate are located in the heating zone provided by the heating means.

United States Patent 72] Inventor William L. Schmitz 835 Huntington Drive, San Marino, Calif. 91108 [21] Appl. No. 872,310 [22] Filed Oct. 29, 1969 [45] Patented Nov. 30, 1971 [54] METAL CASTING APPARATUS 6 Claims, 4 Drawing Figs. [52] US. Cl 164/337, 164/255, 249/54, 266/38, 222/556 [51] lnt.Cl ...B22d 27/16 [50] Field of Search 1. 164/258, 255, 337, 251, 51, 376; 222/556; 266/38 [56] References Cited UNITED STATES PATENTS 2,685,718 8/1954 Schmitz 164/D1G. 9 2,754,347 7/1956 Wroughton et a1. 164/251 X 2,013,653 9/1935 Hoke 164/51 X 3,435,884 4/1969 Orris et a1. 164/337 X Primary Examiner.l. Spencer Overhoiser Assistant Examiner V. K. Rising AlmrneyAllan D. Mockabee METAL CASTING APPARATUS Prior Art The present invention is an improvement upon the casting apparatus disclosed in my prior US. Pat. No. 2,685,718, issued Aug. lO, 1954.

DISCLOSURE This invention relates to casting apparatus and more particularly to the construction of a crucible and gate to be used in conjunction with the mold, for heating molten materials, primarily metals, wherein the structure is such that the molten material is quickly and efficiently discharged from the crucible to a mold located closely therebelow.

Another object of the invention is to provide casting apparatus wherein there is a crucible with a bottom outlet and a are uniform and do not have particles therein which are foreign to the particular metal or alloy being cast.

A further object of the invention is to provide a crucible with a simple yet effective closure gate for the outlet of the crucible wherein means is provided for maintaining the gate in its normal closed position.

Another object is to provide a construction for adjustably supporting the crucible to accommodate molds of different heights.

The above and other objects will more fully appear from the following description in connection with the accompanying drawing:

FIG. 1 is a vertical sectional view through an embodiment of the device;

FIG. 2 is a section taken approximately on the line 2-2 of FIG. 1 with the crucible gate closed;

FIG. 3 is a view similar to FIG. 2 but with the crucible gate in an open position;

FIG. 4 is a fragmentary detail of a portion of the crucible supporting means for alternate positions in full and broken lines.

In my prior patent there is disclosed and claimed apparatus by means of which castings are made while the mold and molten metal are maintained under negative pressure to insure proper filling of the mold, and to eliminate porous or pitted castings.

My prior patent shows a base in a casing 11 and in the top of which there is formed a depression 12 in which depresnegative pressure. Preferably, covered by a screen 20.

Also shown in my prior patent is a mold 24 having a tubular impervious shell 26 filled with a porous molding material 28, such as a conventional self-hardening dental investment. A mold cavity 30 may be formed therein by the usual lost wax method and a bore 32 connects the cavity 30 with a cup 34 formed in the upper face of the molding material 28. All of this structure, or structure similar thereto, is shown in my prior patent.

The shell 26 has an inwardly disposed bead 36 which closely fits the main outer wall portion 38 of the block of porous molding material 28, the latter having an upper enlarged portion 40 defining a shoulder said sleeve 26 and the molding material 28 above the cavity 30 to prevent undesirable bypassing of airflow between the sleeve 26 and the molding material 28.

Adapted to rest upon the upper end of the sleeve 28 is the enlarged and apertured outer end 42 of an arm 44 which is carried by a supporting post 47. Resting upon said enlarged end 42 is a vertically disposed crucible sleeve 46 having an enlarged lower end 48 and a reduced diameter upper end 50 which lies about a graphite crucible 52. Removably resting upon the top of the crucible sleeve 46 is a ceramic cover 54 in which is a fused quartz window 56.

The graphite crucible 52 has a bottom outlet 58 which may be closed by a pair of gate elements 60 which are of concavoconvex shape, the convex portions of which are disposed upwardly and closely fit concave portions 62 formed on the underside of the crucible bottom. The gates 60 partially rotate about pins 64 which are supported by and extend inwardly from the enlarged bottom portion 48 of the sleeve 46. Each gate 60 has a projecting lug 66 which extends through a notch 68 in the crucible sleeve bottom 48 and the outer end of each projecting lug 66 extends into a fork 70 on each end of a pair of fork arms 72, which extend horizontally from a lever 74 pivoted at 76 between a pair of spaced lugs 78 on the upper end of a bolt 80 which extends downwardly through the vertical post 47.

The post 47 extends downwardly into the housing 11 through a sleeve 82 which is welded in the housing as at 84. Said post 46 in its lower portion is provided with a vertical groove 86 having vertically spaced depressions 88, and extending partially around the post from the vertical groove 86 and at the same height as the depressions 88, are grooves 90. Extending from the right side of the base 10 is a sleeve 92 carrying a spring pressed pin 94 which fits into the grooves 86 and and also is removably receivable in the depressions 88. When a handle 96 on the horizontal lever 74 is swung counterclockwise, as viewed in FIG. 4, the post 47 will rotate and cause the vertical groove 86 to align with the pin 94. In this position of FIG. 4. In this position the entire crucible assembly is swung 90 counterclockwise from its position over the mold 28. it is clear that the horizontal lever 74 and handle 96 can be raised, causing the post 46 to raise with them and the crucible can be adjusted to higher elevations than that indicated in FIG. 1. This is to provide accommodation for larger mold elements. For example, one ofgreater diameter and height would rest on the rubber ring 98 and an even wider and higher mold would be received on the rubber ring 100. The molds of course would be of heights to be accommodated by the vertical adjustment of the post 47.

Around the crucible sleeve portion 50 is a coil 102 in the form of an electrical conductor which heats by induction the graphite crucible liner 52 which is a susceptor for the induction heater, and the graphite susceptor 52 in turn heats the gold or other material in the crucible to be molded and cast. While I prefer induction heating because of the speed at which gold and other metals can be melted, it is of course to be understood that other types of heating can be utilized if desired.

It should be noted that the upper is raised by the hand of the user.

The upper surfaces of the gate elements 62 closely fit the underside of the crucible and the fit is such that molten metals heated in the crucible will not leak out when the gate elements are closed.

The gate elements 60 when closed are shown located approximately no lower than the bottom of the heating coil 102 so that the molten metal is maintained in its molten condition immediately at the gate and has no opportunity to cool objectionably when it is dropped from the crucible to the mold. This is important in the case of some metals such as gold wherein a temperature change of to 50 F. below the heat required to keep it molten will permit the gold to solidify. Consequently, the feed from the crucible to the mold must be short in distance as well as time. For that reason the arrangement of the concavo-convex crucible gates and their location with respect to the bottom interior portion of the crucible and the heating coil are rather critical.

There are other methods which are used in casting gold for dentistry, these being the centrifugal method and the air pressure method. The centrifugal method of casting is not practical where vacuum casting is utilized because of the difficulty in maintaining the reduction of pressure in conjunction with a rapidly rotating mold. The use of the vacuum is important and advantageous because it eliminates bubbles in the casting which are quite objectionable in dental inlays and other molded shapes. In the centrifugal casting type of apparatus the upper portion of the pool of molten metal leaves the crucible first and carries with it foreign matter, such as slag, oxides, carbon flux, into the mold, contaminating the casting.

It should be noted that in my apparatus when the molten metal, such as gold, drops through the gate elements 60, the sprue hole 32 is sealed by gold. The application of negative pressure to the somewhat porous mold material 28 removes air from within the mold cavity 30 while the molten gold is flowing into it, so that the cavity is completely filled with the molten metal before it has time to solidify. The rapid reduction of pressure or removal of air from the mold cavity is considerably assisted by the seal provided by the internal bead 36 in the mold sleeve 26 and the houlder formed by the enlarged upper portion 40 of the mold material 28. This is the only seal needed in the apparatus. The crucible being subjected to ordinary atmospheric pressure, no seal is required for the gates 60 and the bottom of the graphite crucible 52.

It will of course be understood that various changes can be made in the form, details, arrangement and proportions of the various parts without departing from the spirit of the invention.

lclaim:

1. Casting apparatus for molten materials including a vertical crucible having a sidewall and having a bottom wall with a concave bottom face having an outlet therethrough, wherein the improvement comprises: electrical heating means lying about the sidewall and the bottom portion of the sidewall; of the crucible, means for supporting said crucible and its bottom outlet above a mold, and a gate supported beneath said crucible in sealing contact with the concave bottom face of said bottom wall about said outlet and pivotally movable in sliding contact with said concave bottom face; from a position closing said bottom outlet to an open position out of vertical alignment with said outlet permitting free gravity drop of molten materials directly from the outlet of the crucible.

2. The structure in claim 1, and the bottom wall of said crucible increasing in thickness radially outwardly from the outlet.

3. The structure in claim 1, surface conforming to the face of said bottom wall.

4. The structure in claim 3, and said gate comprising a pair of jaws movable toward each other to a closed position and away from each other to an open position.

5. The structure in claim 4, and means connected to said gate jaws to actuate the same, said means including means biasing said jaws to a closed position.

6. The structure in claim 1, said crucible outlet being located at the apex of said concave bottom face, and said gate having a convex surface conforming in curvature to the concave bottom face of the bottom wall of the crucible, and said mold positioned directly beneath said gate and said outlet.

and said gate having a convex curvature of the concave bottom 

1. Casting apparatus for molten materials including a vertical crucible having a sidewall and having a bottom wall with a concave bottom face having an outlet therethrough, wherein the improvement comprises: electrical heatinG means lying about the sidewall and the bottom portion of the sidewall; of the crucible, means for supporting said crucible and its bottom outlet above a mold, and a gate supported beneath said crucible in sealing contact with the concave bottom face of said bottom wall about said outlet and pivotally movable in sliding contact with said concave bottom face; from a position closing said bottom outlet to an open position out of vertical alignment with said outlet permitting free gravity drop of molten materials directly from the outlet of the crucible.
 2. The structure in claim 1, and the bottom wall of said crucible increasing in thickness radially outwardly from the outlet.
 3. The structure in claim 1, and said gate having a convex surface conforming to the curvature of the concave bottom face of said bottom wall.
 4. The structure in claim 3, and said gate comprising a pair of jaws movable toward each other to a closed position and away from each other to an open position.
 5. The structure in claim 4, and means connected to said gate jaws to actuate the same, said means including means biasing said jaws to a closed position.
 6. The structure in claim 1, said crucible outlet being located at the apex of said concave bottom face, and said gate having a convex surface conforming in curvature to the concave bottom face of the bottom wall of the crucible, and said mold positioned directly beneath said gate and said outlet. 